Manfrotto 393 question

Recently at a Swan viewing area I was at, a guy had a 60D with the 600 F4 mounted on the Manfrotto 393 cradle. This sure seemed like a great setup for a viewing location like the one I was at where the birds are coming into a fairly small predictable area.
Do you think the 393 mount would work good using only a 400L 5.6 lens? I know this lens is light enough to handhold but it seems like it would be nice to use as it sure made it look easy to tilt and pan the way this gentleman was doing.
I just ordered my first Canon product, a 7D, which will be here next week and I'll be ordering the 400L 5.6 within the next couple of weeks.
Any input would be appreciated.
Thank you.
Bob

It'll work fine. The plate slides through the mounting bracket so you can get optimum balance no matter the lens you're using.

I had the Manfrotto 393, it was too heavy and bulky for me. I think 393 is as heavy as the 400mm, so might not be good for balancing 400mm with 7d.

Are there any other similar designed cradles that you would recommend as I'm totally new to these type of mounts?
Thanks.

well depend on budget. I use Markins q10 with Wimberley sidekick and it works great. if budget is an issue then 393 is good too.